19 research outputs found
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Misorientation-angle-dependent electrical transport across molybdenum disulfide grain boundaries
Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. Here, we explore misorientation angle-dependent electrical transport at grain boundaries in monolayer MoS2 by correlating the atomic defect structures of measured devices analysed with transmission electron microscopy and first-principles calculations. Transmission electron microscopy indicates that grain boundaries are primarily composed of 5–7 dislocation cores with periodicity and additional complex defects formed at high angles, obeying the classical low-angle theory for angles <22°. The inter-domain mobility is minimized for angles <9° and increases nonlinearly by two orders of magnitude before saturating at ∼16 cm2 V−1 s−1 around misorientation angle≈20°. This trend is explained via grain-boundary electrostatic barriers estimated from density functional calculations and experimental tunnelling barrier heights, which are ≈0.5 eV at low angles and ≈0.15 eV at high angles (≥20°)
Self-reported pain scores as a predictor of preterm birth in symptomatic twin pregnancy: a retrospective study
Background
To evaluate the self-reported pain scores as a predictor of preterm birth (PTB) in symptomatic twin pregnancy and to develop a nomogram for the prediction model.
Methods
We conducted a retrospective study of 148 cases of symptomatic twin pregnancies before 34 weeks of gestation visited at Seoul national university hospital from 2013 to 2018. With other clinical factors, self-reported pain score was evaluated by the numerical rating scale (NRS) pain scores for pain intensity. By multivariate analyses and logistic regression, we developed a prediction model for PTB within 7 days. Using the Cox proportional hazards model, the curves were plotted to show the predictability of the PTB according to NRS pain score, while adjusting the other covariates.
Results
Twenty-three patients (15.5 %) delivered preterm within 7 days. By a logistic regression analysis, higher NRS pain score (OR 1.558, 95 % CI 1.093–2.221, P < 0.05), shorter cervical length (OR 3.164, 95 % CI 1.262–7.936, P < 0.05) and positive fibronectin results (OR 8.799, 95 % CI 1.101–70.330, P < 0.05) affect PTB within 7 days. Using the variables, the area under the receiver operating characteristic curve (AUROC) of the prediction model was 0.917. In addition, we developed a nomogram for the prediction of PTB within 7 days.
Conclusions
Self-reported pain scores combined with cervical length and fetal fibronectin are useful in predicting impending PTB in symptomatic twin pregnancy.This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HI19C0213)
Successful pregnancy following transmyometrial embryo transfer after robot-assisted radical trachelectomy
Radical trachelectomy is a fertility-preserving alternative to radical hysterectomy in carefully selected young women with early-stage cervical cancer. However, in cases with subsequent severe cervical stenosis, assisted reproductive techniques can be difficult. This is a case report of a 34-year-old patient who underwent robot-assisted radical trachelectomy and cerclage for early-stage (IB2) adenosquamous carcinoma. Three months after surgery, the patient underwent ovarian stimulation using a gonadotropin-releasing hormone antagonist protocol. As it was impossible to perform transcervical embryo transfer due to the almost complete absence of the cervical opening, transmyometrial embryo transfer under ultrasound guidance was performed. This resulted in a successful singleton pregnancy. This is the first case of successful pregnancy conceived by in vitro fertilization with transmyometrial embryo transfer in a patient who had previously undergone robot-assisted radical trachelectomy.Y
Nondestructive Characterization of Graphene Defects
An effective method is reported for oxidizing graphene/copper fi lm in which
air oxidation of the underlying copper fi lm occurs through the grain boundary
lines of graphene without oxidizing graphene. This oxidation is realized by
partially immersing the graphene/copper fi lm in sodium chloride solution.
Electrons generated during etching of the graphene/copper fi lm in electrolyte
diffuse into the fi lm in contact with air, which eventually enhances air
oxidation of copper through the graphene layer. While the graphene layer
acts as a protective layer against oxidation of the copper fi lm, oxidation of the
underlying Cu fi lm near graphene grain boundary lines is observed by optical
microscopy. This observation could be attributed to the selective diffusion of
oxygen radicals through isolated defects and graphene grain boundaries. The
process involves no appreciable oxidation of the graphene layer including the
graphene grain boundary, as confi rmed by use of detailed Raman and X-ray
photoelectron spectroscopy.
DOI: 10.1002/adfm.201300493
T.124261sciescopu
Observing Grain Boundaries in CVD-Grown Mono layer Transition MetalDichalcogenides
Two-dimensional monolayer transition metal dichalcogenides (TMdCs), driven by graphene
science, revisit optical and electronic properties, which are markedly different from bulk
characteristics. These properties are easily modified due to accessibility of all the atoms viable to
ambient gases, and therefore there is no guarantee that impurities and defects such as vacancies,
grain boundaries, and wrinkles behave as those of ideal bulk. On the other hand, this could be
advantageous in engineering such defects. Here, we report a method of observing grain boundary
distribution of monolayer TMdCs by a selective oxidation. This was implemented by exposing
directly the TMdC layer grown on sapphire without transfer to ultraviolet light irradiation under
moisture-rich conditions. The generated oxygen and hydroxyl radicals selectively functionalized
defective grain boundaries in TMdCs to provoke morphological changes at the boundary, where
the grain boundary distribution was observed by atomic force microscopy and scanning electron
microscopy. This paves the way towards the investigation of transport properties engineered by
defects and grain boundaries.143451sciescopu
Misorientation-angle-dependent electrical transport across molybdenum disulfide grain boundaries
Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. Here, we explore misorientation angle-dependent electrical transport at grain boundaries in monolayer MoS2 by correlating the atomic defect structures of measured devices analysed with transmission electron microscopy and first-principles calculations. Transmission electron microscopy indicates that grain boundaries are primarily composed of 5-7 dislocation cores with periodicity and additional complex defects formed at high angles, obeying the classical low-angle theory for angles = 20 degrees)132371sciescopu
Misorientation-angle-dependent electrical transport across molybdenum disulfide grain boundaries
Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. Here, we explore misorientation angle-dependent electrical transport at grain boundaries in monolayer MoS(2) by correlating the atomic defect structures of measured devices analysed with transmission electron microscopy and first-principles calculations. Transmission electron microscopy indicates that grain boundaries are primarily composed of 5–7 dislocation cores with periodicity and additional complex defects formed at high angles, obeying the classical low-angle theory for angles <22°. The inter-domain mobility is minimized for angles <9° and increases nonlinearly by two orders of magnitude before saturating at ∼16 cm(2) V(−1) s(−1) around misorientation angle≈20°. This trend is explained via grain-boundary electrostatic barriers estimated from density functional calculations and experimental tunnelling barrier heights, which are ≈0.5 eV at low angles and ≈0.15 eV at high angles (≥20°)
Tailoring oxidation of Al particles morphologically controlled by carbon nanotubes
Aluminum powder is used for energetic materials due to high energy density. Controlling oxidation rate, oxidation temperature, and reaction enthalpy is important parameters prior to practical use. Here, we engineered static and dynamic properties of oxidation of Al particles by mixing CNTs (carbon nanotubes) having high thermal conductivity and large exothermic energy. Morphologies of Al/CNT mixture were engineered by a mechanical pulverization. Among various morphologies of Al/CNT mixture of i) CNTs adhered on the surface of Al particles, ii) CNTs partially embedded onto Al particles, forming an urchin type, and iii) CNTs fully embedded into aggregated Al particles, urchin type Al/CNT revealed the largest exothermic enthalpy at the lower oxidation temperature for both γ-Al2O3 and α-Al2O3 phases. This was attributed to the fast heat transfer into Al particles via partially embedded CNTs. Large exothermic enthalpy as well as the mass of alumina were obtained in oxidation of Al/CNT mixture compared to pure Al particles up to 1000°C oxidation. The exothermic enthalpy showed strong dependence on the CNT content, increasing to-188kJ/g at 20wt% CNT. The engineering ability of thermal properties in Al particles with CNTs opens a new research area for diverse use of solid fuel Al. © 2013.1891sciescopu
Oxidation Effect in Octahedral Hafnium Disulfide Thin Film
Atomically smooth van der Waals materials are structurally stable in a monolayer and a few layers but are susceptible to oxygen-rich environments. In particular, recently emerging materials such as black phosphorus and perovskite have revealed stronger environmental sensitivity than other two-dimensional layered materials, often obscuring the interesting intrinsic electronic and optical properties. Unleashing the true potential of these materials requires oxidation-free sample preparation that protects thin flakes from air exposure. Here, we fabricated few-layer hafnium disulfide (HfS2) field effect transistors (FETs) using an integrated vacuum cluster system and study their electronic properties and stability under ambient conditions. By performing all the device fabrication and characterization procedure under an oxygen- and moisture-free environment, we found that few-layer AA-stacking HfS2-FETs display excellent field effect responses (I-on/I-off approximate to 10(7)) with reduced hysteresis compared to the FETs prepared under ambient conditions. Oxidation of HfS2 occurs uniformly over the entire area, increasing the film thickness by 250% at a prolonged oxidation time of >120 h, while defects on the surface are the preferential initial oxidation sites. We further demonstrated that the stability of the device in air is significantly improved by passivating FETs with BN in a vacuum cluster. © 2016 American Chemical Society130331sciescopu